Effect of PACAP on LH release studied by cell immunoblot assay depends on the gender, on the time of day and in female rats on the day of the estrous cycle

We have previously demonstrated that pituitary adenylate cyclase activating polypeptide (PACAP) can be released from cultured rat anterior pituitary cells and when added to the medium in physiological concentration it releases LH from individual gonadotropes. In the present work, we studied whether the release of PACAP and the responsiveness of LH cells to PACAP depend on the gender, on the time of day when the animals were sacrificed, and in females on the stage of the estrous cycle. Anterior pituitary cells were cultured on nitrocellulose membrane. We found that the number of PACAP releasing cells was higher in proestrous than in diestrous female or in male rats and their number was always higher in the evening than at the other times. The effect of PACAP on LH cells was stimulatory in the morning of proestrus and diestrus. In proestrous rats, PACAP did not influence LH release in the afternoon or the evening, but in diestrous rats it decreased it in the afternoon and the evening. In males, there was a decrease of LH due to PACAP treatment at 10 and 20 h; however, PACAP did not influence LH at 16 h. It was concluded that in vivo PACAP might be involved in the circadian and episodic release of LH at pituitary level.

Cell immunoblot assay study demonstrating the release of PACAP from individual anterior pituitary cells of rats and the effect of PACAP on LH release

The presence of pituitary adenylate cyclase activating polypeptide (PACAP) was previously demonstrated in the anterior pituitary by radioimmunoassay, immunohistochemistry, and reverse transcript-polymerase chain reaction (RT-PCR). With the use of cell immunoblot assay (CIBA), when the pituitary cells were cultured on nitrocellulose membrane, the release of PACAP by individual anterior pituitary cells was observed. The released peptide, trapped by the nitrocellulose membrane forming a blot around the cells, was demonstrated by immunocytochemistry. Double labeling revealed that a part of PACAP-immunoreactive cells can release LH as well. With the use of sandwich enzyme immunoassay (S-EIA), it was found that the concentration of PACAP in the anterior pituitaries is 10(-10) M. In cell culture in a similar concentration, PACAP stimulated the LH release from female gonadotropes, but did not influence it from male ones. The stimulated release of LH was indicated by the enhancement in the diameter of LH blots compared to the untreated control cultures. We concluded that PACAP may be released from the anterior pituitary cells in a concentration which would be able to influence LH release not only in vitro but under in vivo conditions as well. The effect of PACAP on LH release was different in female and male pituitary cultures.

Prolactin-synthesizing and prolactin-releasing activity of fetal and early postnatal rat pituitaries: in vivo and in vitro studies using RIA, reverse hemolytic plaque assay and immunocytochemistry

In vivo and in vitro prolactin (PRL)-synthesizing and PRL-releasing activity of fetal (days 12-22) and early postnatal (days 1-10 after birth) rat pituitaries were studied by means of radioimmunoassay (RIA), reverse hemolytic plaque assay and immunocytochemistry. Using RIA, PRL could first be detected, both in the pituitary and in the serum, on day 17 of fetal development. From this day on, pituitary PRL gradually increased, the rise was particularly marked during the postnatal period and became depressed for the first 10 days of postnatal life. On fetal day 18, 12-15% of monodispersed pituitary cells displayed PRL immunopositivity, but only 3-5% of PRL-positive cells were plaque-forming, i.e. released PRL. By the end of gestation 19-25% and on postnatal day 10 42-45% of all pituitary cells were PRL cells and 31-35 and 15-17% of PRL-positive cells, respectively released PRL. Both pre- and postnatal PRL cells in monolayers were insensitive to TRH treatment. Pituitary primordia immunocytochemically and radioimmunologically negative for PRL (13- to 14-day-old fetal) when placed in serum-free organ culture were able to synthesize and release PRL. Fetal pituitary exhibited a highly regular increasing pattern of daily PRL release during a 7-day-culture period. Data obtained both in vivo and in vitro did not exhibit any sex differences. The present findings are consistent with all those observations suggesting an early emergence of fetal rat pituitary lactotrophs. The in vitro results support the concept that Rathke's pouch cells have substantial degree of independence from extrapituitary regulatory actions in the expression and further progression of specific functions.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of intratesticular administration of anti-corticotropin-releasing factor antiserum (a-CRF) on testicular function in neonatal rats

The possible physiological role of testicular corticotropin-releasing factor (CRF) in the regulation of testicular functions was studied in neonatal rats. Two microlitres of anti-CRF-antiserum (dilution: 1:10 or 1:100) was injected intratesticularly to 5 d-old rats with two testes and to hemicastrates. Five days after hemicastration and treatment of the remaining testis with the antiserum, serum testosterone concentration and basal testosterone secretion in vitro decreased significantly. Unilateral testicular injection of a-CRF in rats with two testes resulted in a significant drop in serum testosterone level with no change in basal testosterone production. Data indicate that in neonatal rats testicular CRF might be a local stimulator of steroidogenesis.

Vasectomy modulates the local effect of intratesticular opioids on the gonad of immature rats

Previous studies indicate that 7 days after testicular administration of naloxone, serum testosterone (T) concentration and basal T secretion in vitro decrease significantly. In neonatal rats, short-term (2 h) intratesticular treatment with 0.3 micrograms (D-Met2-Pro5)-enkephalinamide suppresses steroidogenesis. In the present study, testicular treatment with naloxone or enkephalinamide was combined with hemivasectomy (which also includes transection of the inferior spermatic nerve). When local treatment with naloxone was combined with vasectomy in 15-day-old rats, the opioid antagonist-induced increase in testicular weight, the decrease in basal T secretion of the treated gonad and the drop in serum T level could not be observed 7 days postsurgery, despite the fact that in immature rats, hemivasectomy, by itself, also reduces steroid secretion. Similarly, in 5-day-old animals, the short-term (2 h) effect of testicular enkephalinamide on T secretion was prevented by vasectomy. These data suggest that local testicular actions exerted by endogenous opioid peptides might be modulated by the inferior spermatic nerve.

Fetal pituitary graft is capable of initiating hormone synthesis in median eminence removed adult rat

Rathke's pouches of 12- and 13-day-old rat embryos were implanted beneath the kidney capsule of adult male rats subjected to the removal of median eminence or to sham-operation. Host animals were sacrificed 28 days after grafting and the implanted pituitaries were processed for immunohistological examination. ACTH, LH-beta, FSH-beta, TSH-beta, GH and PRL immunopositive cells could be observed in fetal grafts of all experimental groups. However, the number and staining intensity of different hormone containing cells largely varied and presumably depended on the hormonal state of host animals. The results indicate that undifferentiated fetal pituitary does not require hypothalamic hypophysiotrophic neurohormones for proliferation and cytodifferentiation and that its development might be modulated by circulating trophic hormones of host animals.

Intratesticular injection of [D-Met2-Pro5]enkephalinamide suppresses testosterone secretion of the testis of immature rat

The possible role of enkephalin in the local control of testicular function was studied in neonatal rats. 5- and 10-day old hemicastrated rats were treated intratesticularly with an enkephalin analog [D-Met2-Pro5]enkephalinamide. In 5-day-old rats local injection of different doses (0.1-0.3 micrograms/testis) of the peptide suppressed basal testosterone secretion in vitro in a dose-dependent manner 2 h posttreatment. Intratesticular administration of naloxone prior to enkephalin treatment prevented the decrease in basal testosterone production induced by the opioid agonist. In 10-day-old animals intratesticular injection of 1.0 and 3.0 micrograms/testis of enkephalinamide reduced serum testosterone concentration and basal testosterone secretion in vitro. Systemic injection of the peptide produced no change in steroidogenesis. These results suggest that enkephalins might be among the intratesticular factors regulating Leydig cell functions.

Effect of simultaneous local injection of 6-hydroxydopamine and naloxone on the testis of neonatal rats

The effect of simultaneous intratesticular injection of the opiate receptor antagonist naloxone and the neurotoxic drug 6-hydroxydopamine (6-OHDA) on testicular growth, compensatory testicular hypertrophy, serum testosterone level and basal testosterone secretion in vitro was studied in neonatal rats. In animals with two testes unilateral intratesticular administration of naloxone alone enhanced, while 6-OHDA alone decreased the weight of the treated gonad. In animals treated simultaneously with these two agents the decrease in testicular weight induced by 6-OHDA was partially prevented by naloxone. In hemicastrated animals intratesticular treatment with naloxone enhanced the extent of compensatory testicular hypertrophy. Treatment of the remaining testis with 6-OHDA + naloxone did not interfere with the diminished compensatory testicular hypertrophy observed following 6-OHDA treatment. Data indicate that naloxone can counteract the degenerative effect of 6-OHDA in animals with two testes but not in hemicastrates.

Cultured fetal rat pituitaries kept in synthetic medium are able to initiate synthesis of trophic hormones

An immunohistochemical study was performed to determine the capacity of early fetal pituitaries to differentiate into specific hormone-synthesizing tissue in the absence of any influence from the central nervous system. Rathke's pouches from rats were removed from their juxtadiencephalic position on day 11 and 12 of gestation and maintained for 2-7 days in a chemically defined culture medium (M 199) without antibiotics and serum supplementation. The immunocytochemical observations provided evidence for the differentiation of ACTH-, TSH-beta-, LH-beta-, FSH-beta-, GH- and PRL-synthesizing cells in the isolated organ cultured from 11 to 12-day-old pituitary primordia. The appearance of specific hormone-synthesizing cells in vitro displayed a delay of 1.5-2 days compared to the day of appearance in vivo, however, the sequential order of developmental events occurred as observed in vivo. The present results suggest that endocrine or neuroendocrine signals are not required for the expression of specific secretory functions of fetal pituitaries, at least at an age of 11-12 days.

Ontogenesis of the three parts of the fetal rat adenohypophysis. A detailed immunohistochemical analysis

The sequential changes in the histological pattern of anterior pituitary cytodifferentiation of the rat are described. The first labeled cells were ACTH positive and were detected in the pars tuberalis on postconceptual day 13. On day 14 ACTH cells also appeared in the ventral periphery of the pars distalis. On fetal day 15 the pars tuberalis anlage was characterized by numerous well-stained ACTH cells and by some weakly labeled FSH-beta, LH-beta, TSH-beta, GH and PRL cells while the pars distalis showed only ACTH positivity. On day 16 of gestation the ACTH cells were equally distributed throughout the whole pars distalis, while LH-beta, FSH-beta, TSH-beta, PRL and GH immunoreactive cells were localized either in the ventral region of the pars distalis only or were evenly distributed throughout the pars distalis. The present immunocytochemical data suggest that in the pars distalis the hypophyseal cell differentiation follows a clear rostrocaudal, ventrodorsal direction and that the time sequence of the functional differentiation of the adenohypophysis is pars tuberalis, pars distalis and pars intermedia.

Hypothalamic GnRH and pituitary gonadotroph relationships during rat fetal life

The ontogeny of hypothalamic GnRH, of pituitary and gonadal receptors and of pituitary LH and FSH was studied in the fetal and neonatal rat. Hypothalamic, hypophyseal and gonadal primordia were dissected from animals ranging in age from postconceptual day 12 to birth. Immunoreactive GnRH was detectable in the hypothalamus from fetal day 12 onwards at a low level until day 17, whereafter hypothalamic GnRH content and concentration increased until birth. GnRH receptors were reliably detectable in the pituitary anlage from fetal day 16 onwards and increased progressively with advancing age whether expressed as content or concentration. Signs of pituitary LH synthesis were evident as early as fetal day 12 but intrapituitary LH levels remained low until fetal day 17 when levels increased progressively until the end of gestation. Pituitary FSH was undetectable until fetal day 19, thereafter rising dramatically until the end of gestation. GnRH binding to testicular and ovarian tissues was undetectable throughout the period of fetal development. The possible relations among the developmental changes in hypothalamic GnRH, pituitary GnRH receptors and gonadotrophins are discussed.

Effect of unilateral or bilateral thyroidectomy on TRH content of hypothalamus halves

The effect of uni- or bilateral thyroidectomy on the thyrotropin-releasing hormone (TRH) content of the mediobasal hypothalamus (MBH) of the two sides was studied in male rats. Both right- and left-side hemithyroidectomy resulted in a significantly increased TRH content in both halves of the MBH. In addition, the total TRH content rise of the MBH was higher after unilateral than after bilateral thyroidectomy. The mechanism of action of uni- or bilateral thyroidectomy on the hypothalamic TRH content is discussed.

Developmental changes of thyroliberin (TRH) in the rat brain

Levels of thyroliberin (TRH) were measured by radioimmunoassay in the hypothalamus and in the extrahypothalamic brain tissue of rats from fetal day 12 up to day 47 of postnatal life. TRH was detectable as early as on day 12 of intrauterine life in both the hypothalamic primordia and the extrahypothalamic brain tissue. The increase of hypothalamic TRH content was marked between fetal days 12 and 15, then up to the end of gestation it exhibited a slower tendency of increase. From fetal day 15 up to postnatal day 2 the TRH content of the hypothalamus was always higher than that of the extrahypothalamic brain. Both hypothalamic and extrahypothalamic TRH content increased up to day 35 of postnatal life.

Depending on the dose 6-OHDA stimulates or inhibits the testis of immature rats

The effect of the neurotoxic drug, 6-hydroxy-dopamine (6-OHDA) on the testicular growth, the compensatory testicular hypertrophy, the testicular cytology and the serum testosterone level was studied in immature rats. Unilateral injection of 33 micrograms of 6-OHDA beneath the testicular capsule in animals with two testes did not alter the weight of the gonads but promoted the development of both testes. Unilateral injection of 333 micrograms of 6-OHDA resulted in a decreased weight and severe atrophy of the treated gonad, while a significant weight gain of the contralateral testis occurred. In hemicastrated rats 33 micrograms of 6-OHDA into the remaining testis caused an enhanced compensatory testicular hypertrophy. When 333 micrograms of 6-OHDA was administered beneath the capsule of the remaining testis a diminished compensatory testicular hypertrophy occurred but no signs of degeneration could be observed. Data indicate that the testicular adrenergic elements play a role in the testicular growth, in the development of compensatory testicular hypertrophy and in the cytodifferentiation of the immature testis.

Changes in hypophyseal luteinizing hormone (LH) content during fetal and early postnatal life, and capacity of fetal and early postnatal pituitaries to synthesize and release LH in vitro

The developmental pattern of hypophyseal luteinizing hormone (LH) during fetal and early postnatal life, and the capacity of fetal and early postnatal pituitaries to synthesize, release and store LH in the absence of any hypothalamic influence were investigated. Pituitary radioimmunoassayable LH was detectable by fetal day 12; its level remained low up to fetal day 17 and thereafter continued to increase up to postnatal day 2 with sharp rises occurring between day 17 and 18 of gestation and after birth. Cultured fetal and early postnatal pituitary primordia were able to synthesize, to release and store the hormone, however, the pattern of these cellular functions varied according to the animal age when explantation was performed. Data derived from cultured pituitaries showed a gradual rise in the daily hormone content of the medium between fetal day 13 to 17. From fetal day 19 onwards, however, the daily discharge of LH decreased. These findings suggest that the fetal and early postnatal pituitary has the capacity to synthesize and release LH, furthermore after a period of independent differentiation hypothalamic signals appear to be required for pituitary hormone release.

Naloxone has a local effect on the testis of immature rats

Local effect of naloxone on testicular weight, compensatory hypertrophy, and differentiation of the testis and serum testosterone level has been studied in immature rats. A single injection of naloxone in a dose of 2 micrograms/testis under the testicular capsule significantly increased the testicular weight, promoted testicular differentiation and enhanced the rate of compensatory hypertrophy of the remaining testis in unilaterally orchidectomized animals. Data suggest that naloxone has a direct effect on the testis of immature rats.